Bleaching cellulosic materials



Patented July 18, 1944 BLEACHING CELLULOSIC MATERIALS Clifford A.Hampel, Niagara Falls, N. Y., assignor to The Mathieson Alkali Works,Inc., New York, N. Y., a corporation of Virginia No Drawing.

Application September 26, 1941,

Serial No. 412,438

produced by the kraft process, the sulfite process Claims.

It has hitherto been proposed to bleach cellulosic materials withaqueous solutions of chlorites. Such bleaching processes have thegeneral advantage that, properly applied, the degradation of the.

cellulosic material normally incident to the use of conventionalbleaching agents, such as chlorine, hypochlorites and permanganates,particularly when a high degree of bleaching is required, is avoided. Myinvention relates to improvements in the bleaching of cellulosicmaterials with chlorites and in completing the bleaching ofmaterialspartially bleached with such conventional bleaching agents.

I have discovered that cellulosic materials can be bleached to anexceptionally high degree, as reflected by whiteness for example,without substantial degradation, as reflected by loss of strength forexample, by subjecting the cellulosic.

material to the joint action of chlorites and persulfates in aqueoussolution at a pH of about3-11. The useful chlorites comprise thechlorites of the alkali metals and the alkaline earth metals, such assodium chlorite, NaClOz, and calcium chlorite, (Ca(Cl O2) 2. The usefulpersulfates comprise the persulfates of the alkali metals, such assodium persulfate, Naisnoa, and potassium persulfate, K2S20a, and thepersulfates of the alkaline earth metals. Temperatures andconcentrations are widely variable. Increased temperature increases therate of bleaching. The ratio of chloriteto persuliate may vary widely,although a molar ratio of 2:1 is generally useful. The consistency ofthe bleaching solution, the ratio of the weight of the cellulosicmaterial to the weight of the- 'solution, may also vary over a widerange. For

example, the bleaching of pulp can be carried out at pulp consistenciesof about 5%, as in conventional practice, or at much higherconsistencies such as l5% and 25%. At higher consistencies, higherconcentrations of chlorite and persulfate can also be used to acceleratethe bleaching rate.

The bleaching is with'advantage carried out at lulose fibers derivedfrom wood or woody material by any of the generally practiced fiberliberation processes and to the bleaching of cellulose fibers commonlyused in textile manufactures. My invention is applicable to thebleaching of wood pulp chlorite.

and the soda process, to the bleaching of cotton linters, of hemp, ofderivatives of cellulose such as rayon and of woven fabrics producedfrom cellu- The bleaching of my invention is useful, with particularadvantage, in a combined operation in which the cellulosic material ispartially bleached with one or more conventional bleaching agents and inwhich the bleaching is completed with a chlorite and a persulfate inaccordance with my invention. The partial or preliminary bleaching canbecarried to a degree short of that at which substantial degradation ofthe cellulosic materials begins and the bleaching then carried to a highdegree to produce a product of the combined steps of exceptionalwhiteness, for example, and of unusually high strength. For example,kraft pulp can usually be bleached to a degree characterized by awhiteness in the range of 70-78 (G. E. reflectometer) withoutsubstantial degradation by conventional practices-with chlorine or ahypo- By applying my invention, such partially bleached pulp can bebrought to a whiteness of 85 or better, for example, without loss ofstrength or'other degradation.

My invention will be further illustrated by the following examples;

Example I r 125 grams ofa kraft pulp were added to 2500 cc.

of an aqueous solution containing 0.96 grams of sodium chlorite and 1.25grams of sodium persulwashed. The following physical tests wereconducted at F. and 50% relative humidity:

Original Bleached p p p p Total available chlorine applied. Q erccntTotal available chlorine consumednfndouu H 1:96 Bursting strength(Mullen) l. 51. 0 50. 7 Tearing strength (Elmendori) 48 50 Tensilestrength (Schopper) 207 191 Brightness (percent reflectance wi l filterm G. E. reflectometer) 78 87. 16

Example II gram or sodium chlorite and 1.25 grams of sodium persulfzitc.This suspension was brought to and maintained at a pH of 7.5 with halfnormalsodium hydroxide, the pH being checked at regular intervals. Thesuspension wasmaintained ata temperature of 7080 C. for two hours andthe pulpwas then separatedand washed; The fol: lowing. physical testsWere relative humidity:

Original Bleached p p p p 'luial available chlorine applied... percent;.J. 1.0 'lotul available chlorine consumed do f 0.31 Bursting strength(Mulleni. 51.0 50.0 'lcuring strength (Elmendorf)..- 48 l 47 'Iensilestrength (SChOpfiil) 207 200v liriuhtness (percent re eetance v with No.l filter in G. E. rcflectomete 78 I 87. 67

.. Example III 125" grams of the same kraft. pulp were added to 2500 cc.of an aqueous solution containing096.

gram of sodium chlorite and"1.25-grams oi sodium persulfate. Thesuspension was bufiered" at a-pI-I of 8.5 with half normal sodium hydroxide, the pH being" checked at"regular intervals.

Thissuspension' was maintained at aftempera,

ture of 75 80 C. for two hours and the pulp was then separated andwashed. The following physical tests were conducted at 70; F. and0%'relativehumidity:

made at 70fF. and 50% or trisodium phosphate'and 1.0 gram of sodiumOriginal Bleahhed P. D D D' h p Total available chlorine applied...percent.. ..i.0 V Total available chlorine consumed do i'. 0; i0Bursting strength (Mullen)'.. .f 4 5 'learing strength (Elmendori 7 J5Tensile strength (Sehopper) 207 Brightness (percent reflectanc 1 40filter in G. E. reflectometer) I 47. 42

.. h ExampleIV- 125 grams of 2500 cc. of an aqueous solution.-containing"4.8v grams of sodium chlorite and6.25 grams of so; diumpersulfate. This suspension was buiTered at a pH 01"9 with half normalsodium hydroxide, the'pI-I being checked at regular intervals.

The suspension-wasmaintained at a tempera.- 1

ture 0L2? C. for two hours and the pulp was then separated and washed.The following phys ical tests were conducted at 70 F. and-% relativehumidity;

Original Bleached pu p p' Total available chlorine applied..- peroent.5.0 Bursting strength (Mullen). 51.0 51.1 'lenring strength (Elmendori).1 48 47 Tensile strength (Schopper)..-. 207 191- Brightness (percentreflectance h N l :filter in G. E. reflecto neter) V 78 83. 91

)7 Example V vkraft 'p ulp w ere suspended in Original Bleached pulppulpv Total available ehlorineapplied. percent" l. 5 Burstingstrength-(.\lullen). 51.0 49.8 Tearing strength (Elmendorf) 48 46Tensile strength (Schopper) 207 217 Brightness (percent reflectance withNo. 1

filter in G. E. reilectometer) -L 78 83. 42

Example Vi 12-5 grains ofanother kraft pulp were added to 2500-"ce'. ofan aqueous solution containing -:-0.96 gram of sodium .chlorite and1.25'grams of sodium persulfate.

The suspension was. buffered at a pH of 9.1 with"half 'norma1 sodiumhydroxide, the pH being checked, at regular intervals. Thissuspensionwasmaintained at :60? C. for. two hours'andrthe pulpv was'thenseparated and washed. ,The followingphysieal tests were made at F.andz50% relative'humidityz Original "Bleached p p: :p p.

Total available chlorine applied .percent. v 1. 0: Bursting strength(Mullen) 51.0 49. 6 'learing strength (Elniendori).... 48 45 -'lensilestrength (Sehoppvr) 207 v I 200 Brightness (percent'reilectance with No.1

filter in G. E. reileetometer) 84. 5

Ercdrnple VII pieceof 'uritreate d greig e cotton muslin, x 80 threadsper inch, weighing 36 grams and measuring 12inches by 38 inches; wasplaced in 500 ccfof water containing 1.5 grams of sodium chlorite, 2.0grains ofsodium persulfate. .LOQgram ethane 1-palmitate 2 -su1fonate.This solution, with the cloth init, was maintained at a temcloth wasthen washed, soured, in aqueous sulfuriea'cid containing 1% jIC lfiSOQrewashed'and ironed dry. The brightness was increased from 5638 to82.5,"the absorbency was good,j,the starch removal was 'quite'complete,all motes had been removed and thejclotl had notheentendered.

" Example VIII 36 gramsof the same muslin in 500 oc.of,wa, a .tercontaining 1.0 gram of sodiurn chlorite, 2

grams of sodium persulfate, 1.0 gram of .trisodiurn phosphateandJLO gramof sodium ethane 1- palmitate 2-s'ulfonate vweren' aintainedat a. tem

perature bf C.1for thirty minutes. I The cloth was then washed, souredwith aqueous1%"I-IaSO rewashed and ironed dry. :The brightness was 1increased from 56.8 to "83.5, the'absorbency was good, starch removalwas quite complete, the- 4 motes had been removed and thecloth had not 1been tendered.

'125 grams of anotherkraft were Inbred. 1

with-840 cc. of an aqueous solution containing 1.44 grams ofsodium-chlorite and 1.5 grams 01 sodium persulfate, bufiered at a'pH of8.5 with half normal sodium hydroxide, the pH being checked at regularintervals. This suspension had a consistency of'15%. .The suspension wasmaintained at a temperature of 35-43 C. for

two hours and the pulp was then separatedand "Exa ple I f 1 36 grams ofthe same. muslin. in=500 cc. of water containing 0.5 gram of sodium'chlorite, 1.0 gram of sodium persulfate,.1.01 gram of trisodiumphosphate and 1.0 gramof'sodium ethane 1-palmitate -2-suifonate weremaintained at "a temperature of.

95C. for one hour, Theeloth wasthen washed, soured with; aqueous 1% Hzsourewa'shed and ironed dry. The brightness was increased from 56.8 to 82.3, the-absorbency was good. the starch and mote-removal was quitecomplete and the "cloth had not been tendered.

washed. The following physical tests'were cond l duced at 70 F. and 50%relative humidity:

l which steam was passed for ten minutes. cloth was then washed andsoaked in an aqueous Example X 18 grams of the same muslin were soakedin an aqueous solution containing grams per liter of sodium chlorite,grams per liter of sodium persulfate and 50 drops per liter of sodiumdiamyl sulfosuccinate as a wetting agent, buffered at a pH of 8;8. Thecloth was then drained until it held about its own weight of solutionand then hung in a vessel through which steam was passed for tenminutes. The cloth was then washed. soured, rewashed and ironed dry. Thebrightness was increased from 56.8 to 78.

Example XI 18 grams of the same muslin were soaked in an aqueoussolution containing 20 grams per liter of sodium hydroxide, 2 grams perliter of sodium chlorite and 50 drops per liter of sodium diamylsulfo'succinate as a wetting agent. The cloth was then drained until itcontained about its own weight of solution and hung in a vessel throughThe solution containing 10 grams per liter of sodium 1 chlorite and 20grams per liter of sodium persulfate, drained until it contained aboutits own ironed dry. The brightness was increased from 56.8 to 83,thestarch and mote removal was quite complete, the absorbency was goodand the cloth had not been tendered.

Example XI! 125 grams of a Swedish kraft pulp were added to 2500 cc. ofan aqueous solution containing 0.19 grain of sodium chlorite and 0.37gram of sodium 1 persulfate. This suspension was buffered at a pH of 8with half normal sodium hydroxide, the pH being checked at regularintervals. The suspension was maintained at a temperature of 60 C.fortwo hours, and the pulp was then separated and washed. The followingphysical tests were In one aspect my invention affords importanteconomies. Many complicated processes involving critical controls oftime, temperature and concentrations have been devised to effect highdegrees of bleaching with minimum degradation but none of them has beenentirely satisfactory when applied to produce high degrees of bl aching,and all of them have been expensive to apply. As compared to a number ofsuch processes, the bleaching process of my invention will produccomparable degrees of whiteness with substantial cost savings andwithout substantial degradation of the cellulosic material. Also, thebleaching process of my invention will produce exceptionally highdegrees of whiteness with relatively short bleaching times as comparedto a number of such processes.

I claim:

1. In the bleaching of cellulosic material, the improvement whichcomprises subjecting the material to be bleached to the action of anaqueous solution containing a compound selected from the groupconsisting of chlorites of the alkali metals and alkaline earth metalsand a compound selected from the group consisting of persuliates ofalkali metals and alkaline earth metals at a pH of about 3-11.

2. In the bleaching of cellulosic material, the improvement whichcomprises completing the bleaching by subjecting partially bleachedmaterial to the action of an aqueous solution contain ing a compoundselected from the group consisting of chlorites of alkali metals andalkaline earth metals and a compound selected from the group consistingof persulfates of alkali metals and alkaline earth metals at a pH ofabout 3-11.

3. In the bleaching of cellulosic material, the improvement whichcomprises subjecting the material to be bleached to the action of anaqueous solution containing a compound selected from the groupconsisting of chlorites of alkali metals and alkaline earth metals and acompound selected from the group consisting of persull'ates of alkalimetals and alkaline earth metals at a pH of about 3-11 and at atemperature of about -80 C.

4. In the bleaching of cellulosic material, the improvement whichcomprises subjecting the material to be bleached to the action of anaqueous solution containing a compound selected from the groupconsisting of alkali metal chlorites and alkaline earth metal chloritesand also containing a. compound selected from the group consisting ofalkali metal persulfates and alkaline earth metal persulfates at a pH ofabout about 7-11 and at a temperature of about 60-80 C.

5. In the bleaching of cellulosic material, the improvement whichcomprises subjecting the material to be bleached to the action of anaqueous solution containing a compound selected from the groupconsisting of alkali metal chlorites and alkaline earth metal chloritesand also containing a compound selected from the group consisting ofalkali metal persulfates and alkaline earth metal persulfates at a pH ofabout 7-11.

CLIFFORD A. HAMPEL.

